Merge pull request #1012 from 0xff-dev/1545

Add solution and test-cases for problem 1545

Author: 6boris

leetcode/1501-1600/1545.Find-Kth-Bit-in-Nth-Binary-String/README.md

@@ -1,28 +1,39 @@
 # [1545.Find Kth Bit in Nth Binary String][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+Given two positive integers `n` and `k`, the binary string `Sn` is formed as follows:
+
+- `S1 = "0"`
+- `Si = Si - 1 + "1" + reverse(invert(Si - 1))` for `i > 1`
+
+Where `+` denotes the concatenation operation, `reverse(x)` returns the reversed string `x`, and `invert(x)` inverts all the bits in `x` (`0` changes to `1` and `1` changes to `0`).
+
+For example, the first four strings in the above sequence are:
+
+- `S1 = "0"`
+- `S2 = "011"`
+- `S3 = "0111001"`
+- `S4 = "011100110110001"`
+
+Return the `kth` bit in `sn`. It is guaranteed that `k` is valid for the given `n`.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: n = 3, k = 1
+Output: "0"
+Explanation: S3 is "0111001".
+The 1st bit is "0".
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Find Kth Bit in Nth Binary String
-```go
 ```
-
+Input: n = 4, k = 11
+Output: "1"
+Explanation: S4 is "011100110110001".
+The 11th bit is "1".
+```
 
 ## 结语
 

leetcode/1501-1600/1545.Find-Kth-Bit-in-Nth-Binary-String/Solution.go

@@ -1,5 +1,24 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(n int, k int) byte {
+	alloc := 1
+	for i := 2; i <= n; i++ {
+		alloc = (alloc * 2) + 1
+	}
+	bs := make([]byte, alloc)
+	bs[0] = '0'
+	index := 1
+	for i := 2; i <= n; i++ {
+		bs[index] = '1'
+		end := index
+		index++
+		for j := end - 1; j >= 0; j-- {
+			bs[index] = '0'
+			if bs[j] == '0' {
+				bs[index] = '1'
+			}
+			index++
+		}
+	}
+	return bs[k-1]
 }

leetcode/1501-1600/1545.Find-Kth-Bit-in-Nth-Binary-String/Solution_test.go

@@ -10,30 +10,29 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		n, k   int
+		expect byte
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", 3, 1, '0'},
+		{"TestCase2", 4, 11, '1'},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.n, c.k)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.n, c.k)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }